What valve is either fully opened or fully closed? They are designed with a backseat and foreseat that prevent refrigerants from bleeding by?

• A. Float switch
• B. Pressure relief valve
• C. Ball valve
• D. Shutoff valve, aka Isolation, Service, or Stop valve

Answer: (D)

Shutoff valves are meant to be either fully open or fully closed, providing a decisive stop in the line. They use a foreseat and a backseat to keep refrigerant from bleeding by the stem packing. The foreseat is the seating surface that the valve plug or disk presses against to stop flow when closed, giving a tight seal. The backseat is inside the bonnet and can seal against the stem to isolate the packing from the line pressure, so maintenance or stem removal won’t let refrigerant leak past the packing. This combination keeps the system watertight around the stem in both positions, preventing refrigerant from escaping through the packing.